1. Field of the Invention
This invention relates to an image forming apparatus such as a printer, a facsimile machine, etc.
2. Description of Related Art
In typical image forming apparatuses of electrophotographic method, a toner as a developer is supplied from a developing device to latent images formed on an image carrier to develop the images. The developing device includes a developing roller serving as a developer carrier for developing at least the latent image on the image carrier upon attaching the developer, and a toner supply roller serving as a supply member for supplying a triboelectrically charged toner to the developing roller while rotating as contacting to the developing roller.
Some device, among such developing devices, has been known as a device counting up the printing sheet number and changing a voltage between a developing roller and a toner supply roller according to the counted sheet number in order to prevent the toner amount attaching to the developing roller from being lowered when the printing sheet number is increased (see e.g., Japanese Patent Application Publication No. H09-171286).
With such a conventional image forming apparatus, however, image failures may occur in accordance with the toner consumption amount.